Effect of transforming growth factor-beta and platelet-derived growth factor-BB on articular cartilage in rats

Bioengineering Approaches for Delivering Growth Factors: A Focus on Bone and Cartilage Regeneration

Growth factors are bio-factors that target reparatory cells during bone regeneration. These growth factors are needed in complicated conditions of bone and joint damage to enhance tissue repair. The delivery of these growth factors is key to ensuring the effectiveness of regenerative therapy. This review discusses the roles of various growth factors in bone and cartilage regeneration. The methods of delivery of natural or recombinant growth factors are reviewed. Different types of scaffolds, encapsulation, Layer-by-layer assembly, and hydrogels are tools for growth factor delivery. Considering the advantages and limitations of these methods is essential to developing regenerative therapies. Further research can accordingly be planned to have new or combined technologies serving this purpose.

Induction of Cartilage Regeneration by Nanoparticles Loaded with Dentin Matrix Extracted Proteins

Due to the limited self-repair capacity of articular cartilage, tissue engineering has good application prospects for cartilage regeneration. Dentin contains several key growth factors involved in cartilage regeneration. However, it remains unknown whether dentin matrix extracted proteins (DMEP) can be utilized as a complex growth-factor mixture to induce cartilage regeneration. In this work, we extracted DMEP from human dentin and improved the content and activity of chondrogenic-related growth factors in DMEP by alkaline conditioning. Afterwards, mesoporous silica nanoparticles (MSNs) with particular physical and chemical properties were composed to selectively load and sustain the release of proteins in DMEP. MSN-DMEP promoted chondrogenic differentiation of rat bone marrow-derived mesenchymal stem cells with fewer growth factors than exogenously added transforming growth factor-β1 (TGF-β1). Therefore, MSN-DMEP may serve as a promising candidate for cartilage regeneration as an alternative to expensive synthetic growth factors.

Microfracture Augmentation With Trypsin Pretreatment and Growth Factor-Functionalized Self-assembling Peptide Hydrogel Scaffold in an Equine Model

BACKGROUND

Microfracture augmentation can be a cost-effective single-step alternative to current cartilage repair techniques. Trypsin pretreatment combined with a growth factor-functionalized self-assembling KLD hydrogel ("functionalized hydrogel") has been shown to improve overall cartilage repair and integration to surrounding tissue in small animal models of osteochondral defects.

HYPOTHESIS

Microfracture combined with trypsin treatment and a functionalized hydrogel will improve reparative tissue quality and integration as compared with microfracture alone in an equine model.

STUDY DESIGN

Controlled laboratory study.

METHODS

Bilateral cartilage defects (15-mm diameter) were created on the medial trochlear ridge of the femoropatellar joints in 8 adult horses (16 defects total). One defect was randomly selected to receive the treatment, and the contralateral defect served as the control (microfracture only). Treatment consisted of 2-minute trypsin pretreatment of the surrounding cartilage, subchondral bone microfracture, and functionalized hydrogel premixed with growth factors (platelet-derived growth factor and heparin-binding insulin-like growth factor 1). After surgery, all horses were subjected to standardized controlled exercise on a high-speed treadmill. Clinical evaluation was conducted monthly, and radiographic examinations were performed at 2, 16, 24, 32, 40, and 52 weeks after defect creation. After 12 months, all animals were euthanized. Magnetic resonance imaging, arthroscopy, gross pathologic evaluation of the joint, histology, immunohistochemistry, and biomechanical analyses were performed. Generalized linear mixed models (with horse as random effect) were utilized to assess outcome parameters. When P values were <.05, pairwise comparisons were made using least squares means.

RESULTS

Improved functional outcome parameters were observed for the treatment group, even though mildly increased joint effusion and subchondral bone sclerosis were noted on imaging. Microscopically, treatment resulted in improvement of several histologic parameters and overall quality of repaired tissue. Proteoglycan content based on safranin O-fast green staining was also significantly higher in the treated defects.

CONCLUSION

Trypsin treatment combined with functionalized hydrogel resulted in improved microfracture augmentation.

CLINICAL RELEVANCE

Therapeutic strategies for microfracture augmentation, such as those presented in this study, can be cost-effective ways to improve cartilage healing outcomes, especially in more active patients.

Trypsin Pre-Treatment Combined With Growth Factor Functionalized Self-Assembling Peptide Hydrogel Improves Cartilage Repair in Rabbit Model

The objective of this study was to improve cartilage repair and integration using self-assembling KLD hydrogel functionalized with platelet-derived growth factor-BB and heparin-binding insulin-like growth factor-1 with associated enzymatic trypsin pre-treatment of the native cartilage. Bilateral osteochondral defects were created at the central portion of the femoral trochlear groove of 48 skeletally mature, white New Zealand rabbits. One limb received a randomly assigned treatment and the contralateral limb served as the control. Treated defects were exposed to trypsin for 2 min and filled with self-assembling KLD hydrogel only, or associated to growth factors. All control limbs received KLD hydrogel alone or received only trypsin but not hydrogel. Ninety days post-defect creation, the rabbits were euthanized and magnetic resonance imaging, radiography, macroscopic evaluation, histology, and immunohistochemistry of the joint and repaired tissue were performed. Mixed model analyses of variance were utilized to assess the outcome parameters and individual comparisons were performed using Least Square Means procedure and differences with p-value < 0.05 were considered significant. Trypsin enzymatic pre-treatment improved cellular morphology, cluster formation and subchondral bone reconstitution. Platelet-derived growth factor-BB improved subchondral bone healing and basal integration. Heparin-binding insulin-like growth factor-1 associated with platelet-derived growth factor improved tissue and cell morphology. The authors conclude that self-assembling KLD hydrogel functionalized with platelet-derived growth factor and heparin-binding insulin-like growth factor-1 with associated enzymatic pre-treatment of the native cartilage with trypsin resulted in an improvement on the cartilage repair process. © 2019 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 37:2307-2315, 2019.

Morphological, Immunocytochemical, and Biochemical Studies of Rat Costal Chondrocytes Exposed to IL-1β and TGF-β1

This study was undertaken to determine the effects of IL-1β and TGF-β1 on the expression of differentiation-associated genes in chondrocytes in vitro. Rat costal chondrocytes were exposed to different concentrations of IL-1β and TGF-β1 for 48 h and tested for gene expression. IL-1β increased the expression of aggrecanase-1 and aggrecanase-2 and decreased the content of aggrecan and collagen II. Low concentration of TGF-β1 decreased the expression of aggrecan and collagen II and increased the expression of aggrecanase-2. However, the level of aggrecanase-1 was significantly elevated in the presence of high concentration of TGF-β1. IL-1β and TGF-β1 show the ability to modulate the production of aggrecan and collagen II in chondrocytes in vitro.

Growth Factor-Mediated Migration of Bone Marrow Progenitor Cells for Accelerated Scaffold Recruitment

Tissue engineering approaches using growth factor-functionalized acellular scaffolds to support and guide repair driven by endogenous cells are thought to require a careful balance between cell recruitment and growth factor release kinetics. The objective of this study was to identify a growth factor combination that accelerates progenitor cell migration into self-assembling peptide hydrogels in the context of cartilage defect repair. A novel 3D gel-to-gel migration assay enabled quantification of the chemotactic impact of platelet-derived growth factor-BB (PDGF-BB), heparin-binding insulin-like growth factor-1 (HB-IGF-1), and transforming growth factor-β1 (TGF-β1) on progenitor cells derived from subchondral bovine trabecular bone (bone-marrow progenitor cells, BM-PCs) encapsulated in the peptide hydrogel [KLDL]3. Only the combination of PDGF-BB and TGF-β1 stimulated significant migration of BM-PCs over a 4-day period, measured by confocal microscopy. Both PDGF-BB and TGF-β1 were slowly released from the gel, as measured using their (125)I-labeled forms, and they remained significantly present in the gel at 4 days. In the context of augmenting microfracture surgery for cartilage repair, our strategy of delivering chemotactic and proanabolic growth factors in KLD may provide the necessary local stimulus to help increase defect cellularity, providing more cells to generate repair tissue.

Systemic neutralization of TGF-β attenuates osteoarthritis

Osteoarthritis (OA) is a major source of pain and disability worldwide with no effective medical therapy due to poor understanding of its pathogenesis. Transforming growth factor β (TGF-β) has been reported to play a role in subchondral bone pathology and articular cartilage degeneration during the progression of OA. In this study, we demonstrated that systemic use of a TGF-β-neutralizing antibody (1D11) attenuates OA progression by targeting subchondral bone pathological features in rodent OA models. Systemic administration of 1D11 preserves the subchondral bone microarchitecture, preventing articular cartilage degeneration by inhibition of excessive TGF-β activity, in both subchondral bone and the circulation. Moreover, the aberrant increases in the numbers of blood vessels, nestin(+) mesenchymal stromal/stem cells, and osterix(+) osteoblast progenitors were normalized by 1D11 systemic injection. Thus, systemic neutralization of excessive TGF-β ligands effectively prevented OA progression in animal models, with promising clinical implications for OA treatment.

Augmentation techniques for isolated meniscal tears

Meniscal tears are relatively common injuries sustained by athletes and non-athletes alike and have far reaching functional and financial implications. Studies have clearly demonstrated the important biomechanical role played by the meniscus. Long-term follow-up studies of post-menisectomy patients show a predisposition toward the development of degenerative arthritic changes. As such, substantial efforts have been made by researchers and clinicians to understand the cellular and molecular basis of meniscal healing. Proinflammatory cytokines have been shown to have a catabolic effect on meniscal healing. In vitro and some limited in vivo studies have shown a proliferative and anabolic response to various growth factors. Surgical techniques that have been developed to stimulate a healing response include mechanical abrasion, fibrin clot application, growth factor application, and attempts at meniscal neovascularization. This article discusses various augmentation techniques for meniscal repair and reviews the current literature with regard to fibrin clot, platelet rich plasma, proinflammatory cytokines, and application of growth factors.

Human chondrogenic paraxial mesoderm, directed specification and prospective isolation from pluripotent stem cells

Directed specification and prospective isolation of chondrogenic paraxial mesoderm progeny from human pluripotent stem (PS) cells have not yet been achieved. Here we report the successful generation of KDR⁻PDGFRα⁺ progeny expressing paraxial mesoderm genes and the mesendoderm reporter MIXL1-GFP in a chemically defined medium containing the canonical WNT signaling activator, BMP-inhibitor, and the Nodal/Activin/TGFβ signaling controller. Isolated (GFP⁺)KDR⁻PDGFRα⁺ mesoderm cells were sensitive to sequential addition of the three chondrogenic factors PDGF, TGFβ and BMP. Under these conditions, the cells showed robust chondrogenic activity in micromass culture, and generated a hyaline-like translucent cartilage particle in serum-free medium. In contrast, both STRO1⁺ mesenchymal stem/stromal cells from adult human marrow and mesenchymal cells spontaneously arising from hPS cells showed a relatively weaker chondrogenic response in vitro, and formed more of the fibrotic cartilage particles. Thus, hPS cell-derived KDR⁻PDGFRα⁺ paraxial mesoderm-like cells have potential in engineered cartilage formation and cartilage repair.

The role of growth factors in cartilage repair

BACKGROUND

Full-thickness chondral defects and early osteoarthritis continue to present major challenges for the patient and the orthopaedic surgeon as a result of the limited healing potential of articular cartilage. The use of bioactive growth factors is under consideration as a potential therapy to enhance healing of chondral injuries and modify the arthritic disease process.

QUESTIONS/PURPOSES

We reviewed the role of growth factors in articular cartilage repair and identified specific growth factors and combinations of growth factors that have the capacity to improve cartilage regeneration. Additionally, we discuss the potential use of platelet-rich plasma, autologous-conditioned serum, and bone marrow concentrate preparations as methods of combined growth factor delivery.

METHODS

A PubMed search was performed using key words cartilage or chondrocyte alone and in combination with growth factor. The search was open for original manuscripts and review papers and open for all dates. From these searches we selected manuscripts investigating the effects of growth factors on extracellular matrix synthesis and excluded those investigating molecular mechanisms of action.

RESULTS

By modulating the local microenvironment, the anabolic and anticatabolic effects of a variety of growth factors have demonstrated potential in both in vitro and animal studies of cartilage injury and repair. Members of the transforming growth factor-β superfamily, fibroblast growth factor family, insulin-like growth factor-I, and platelet-derived growth factor have all been investigated as possible treatment augments in the management of chondral injuries and early arthritis.

CONCLUSIONS

The application of growth factors in the treatment of local cartilage defects as well as osteoarthritis appears promising; however, further research is needed at both the basic science and clinical levels before routine application.

Local administration of autologous synovium-derived cells improve the structural properties of anterior cruciate ligament autograft reconstruction in sheep

BACKGROUND

The structural properties of a tendon autograft deteriorate during the remodeling phase after anterior cruciate ligament (ACL) reconstruction.

HYPOTHESIS

A local application of autologous synovium-derived cells cultured in medium supplemented with transforming growth factor β (TGFβ) may inhibit the deterioration of structural properties of the tendon graft after ACL reconstruction.

STUDY DESIGN

Controlled laboratory study.

METHODS

Fifty-two mature sheep were used. In each animal, the right knee underwent ACL reconstruction using the semitendinosus tendon autograft; then, the animals were divided into 5 groups of 10. No additional treatments were applied in group 1, whereas fibrin sealant was applied around the graft in group 2. In group 3, autologous synovium-derived cells cultured in standard medium were applied around the graft with fibrin sealant, whereas autologous synovium-derived cells cultured in TGFβ-supplemented medium were applied with fibrin sealant in group 4. In group 5, fibrin sealant containing 20 ng of TGFβ was applied around the graft. Each animal was sacrificed at 12 weeks after the surgery. In each group, 7 and 3 sheep were used for biomechanical and histologic evaluations, respectively. The remaining 2 sheep were used to confirm whether the applied cells infiltrated the graft at 1 week after surgery.

RESULTS

Confocal microscope observations showed that the applied cells that were labeled before implantation infiltrated into the superficial portion of the graft at 1 week. Biomechanically, the maximum load and the stiffness of groups 4 and 5 were significantly greater than those of groups 1, 2, and 3. Histologically, necrotic lesions were observed in the core portion of the midsubstance in groups 1 and 2. In groups 3, 4, and 5, no necrotic lesions were found in the midsubstance.

CONCLUSION

A local application of autologous synovium-derived cells cultured in TGFβ-supplemented medium or a fibrin sealant containing TGFβ significantly inhibits the natural deterioration of the structural properties of the tendon graft after ACL reconstruction.

CLINICAL RELEVANCE

Administration of autologous synovium-derived cells cultured in TGFβ-supplemented medium or TGFβ and fibrin glue alone can be a potential cell-based therapy to prevent graft deterioration after transplantation or accelerate mechanical restoration of the deteriorated graft.

Is platelet-derived growth factor-BB expression proportional to fibrosis in the hypertrophied lumber ligamentum flavum?

STUDY DESIGN

A clinical and experimental assessment using human samples of lumbar ligamentum flavum (LF).

OBJECTIVE

To identify platelet-derived growth factor-BB (PDGF-BB) expression in hypertrophied LF of patients with lumbar spinal canal stenosis (LSS) and relate it to fibrosis.

SUMMARY OF BACKGROUND DATA

Recent studies showed that fibrosis in LF hypertrophy was due to accumulation of inflammation-related scar tissue. PDGF-BB participates in scar formation and collagen development in wound healing and fibrosis diseases. However, it is unclear whether PDGF-BB expression is associated with fibrosis of the hypertrophied LF in LSS.

METHODS

In all, 10 patients of LSS was enrolled in this study, while 10 patients of lumbar disc herniation (LDH) as a control group. LF thickness was measured by axial T1-weighted magnetic resonance imaging. Fibrosis was graded and type of collagen was identified. The location and the expression of PDGF-BB were analyzed using immunohistochemical stains, real-time polymerase chain reaction, and Western Blotting. Correlation among LF thickness, fibrosis, and PDGF-BB expression was analyzed.

RESULTS

LF thickness was 5.3 ± 1.0 mm (range from 3.9 to 7.5 mm) in the LSS group and 2.8 ± 0.7 mm (range from 1.69 to 3.8 mm) in the LDH group. Obvious fibrosis was observed in all samples of the LSS group, and correlated to LF thickness of the dural, middle, and dorsal layers (P < 0.05), respectively. PDGF-BB was detected in the hypertrophied LF, particularly in the dorsal layer. PDGF-BB expression was higher in the LSS group than that in the LDH group (P < 0.05), and in the dorsal layer than the dural layer in the LSS group (P < 0.05). PDGF-BB mRNA correlated significantly to thickness of LF (r = 0.41) and the severity of fibrosis (r = 0.69) (P < 0.05).

CONCLUSION

A higher PDGF-BB expression existed in the hypertrophied LF of patients with LSS and could be a risk factor of the fibrosis.

Additive effects of hyperbaric oxygen and platelet-derived growth factor-BB in chondrocyte transplantation via up-regulation expression of platelet-derived growth factor-beta receptor

The present study investigated the effects of hyperbaric oxygen (HBO) and platelet-derived growth factor-BB (PDGF-BB) in chondrocyte transplantation. In vitro, chondrocytes were treated with HBO, PDGF-BB, and HBO combined with PDGF-BB (H+P). Cell growth was analyzed using cell counting, MTT assay, and FACS analysis. mRNA expression of the PDGF-alpha receptor (PDGFR-alpha) and beta receptor (PDGFR-beta) was detected by RT-PCR. Protein expression of PDGFR-beta was detected by Western blotting. In vivo, chondrocytes and PDGF-BB were suspended in alginate as a transplantation system. Cartilage defects were grafted with this system and with or without HBO treatment. Released PDGF-BB concentration was quantified by ELISA. After 8 weeks, animals were sacrificed and the repaired tissues were examined. In vitro data suggested that each treatment increased cell growth via the up-regulated mRNA expression of PDGFR-alpha and increased cell accumulation in the S-phase. The H+P treatment was more additive in cell growth and in mRNA and protein expression of PDGFR-beta than HBO or PDGF-BB. In vivo results suggested that PDGF-BB delivery lasted for more than 5 weeks. Scoring results showed that each treatment significantly increased the cartilage repair. Safranin-O and type II collagen staining confirmed the hyaline-like cartilage regeneration in the repaired tissues. In situ up-regulation of PDGFR-beta expression partially explains the additive effect of H+P treatment in cartilage repair. Accordingly, H+P offers a potential treatment method for cartilage repair.

Leptin plays a catabolic role on articular cartilage

Leptin has been shown to play a crucial role in the regulation of body weight. There is also evidence that this adipokine plays a key role in the process of osteoarthritis. However, the precise role of leptin on articular cartilage metabolism is not clear. We investigate the role of leptin on articular cartilage in vivo in this study. Recombinant rat leptin (100 μg) was injected into the knee joints of rats, 48 h later, messenger RNA (mRNA) expression and protein levels of basic fibroblast growth factor (bFGF), vascular endothelial growth factor (VEGF), matrix metalloproteinases 2 and 9 (MMP-2, MMP-9), cathepsin D, and collagen II from articular cartilage were analyzed by real-time quantitative polymerase chain reaction (PCR) and western blot. Two important aggrecanases ADAMTS-4 and -5 (a disintegrin and metalloproteinase with thrombospondin motifs 4 and 5) were also analyzed by real-time quantitative PCR. Besides, articular cartilage was also assessed for proteoglycan/GAG content by Safranin O staining. Leptin significantly increased both gene and protein levels of MMP-2, MMP-9, cathepsin D, and collagen II, while decreased bFGF markedly in cartilage. Moreover, the gene expression of ADAMTS-4 and -5 were markedly increased, and histologically assessed depletion of proteoglycan in articular cartilage was observed after treatment with leptin. These results strongly suggest that leptin plays a catabolic role on cartilage metabolism and may be a disadvantage factor involve in the pathological process of OA.

Smurf2 induces degradation of GSK-3beta and upregulates beta-catenin in chondrocytes: a potential mechanism for Smurf2-induced degeneration of articular cartilage

We have previously demonstrated that Smurf2 is highly expressed in human osteoarthritis (OA) tissue, and overexpression of Smurf2 under the control of the type II collagen promoter (Col2a1) induces an OA-like phenotype in aged Col2a1-Smurf2 transgenic mice, suggesting that Smurf2 is located upstream of a signal cascade which initiates OA development. However, the factors downstream of Smurf2 in this signal cascade and how Smurf2-induced OA is initiated are largely unknown. In this study, we further characterized the phenotypic changes in Col2a1-Smurf2 transgenic and WT articular cartilage from the postnatal stage to adulthood. We found that the articular cartilage degeneration occurring at the cartilage surface in 6 month-old Col2a1-Smurf2 transgenic mice progressed from an expanded hypertrophic domain in the basal layer of the deep articular cartilage at 2.5 weeks of age, which may lead to an accelerated calcification and ectopic ossification of this region at 1 month of age, and aggregation and maturation of articular chondrocytes in the middle and deep zones at 2 months and 4.5 months of age, respectively. Furthermore, we discovered that ectopically expressed Smurf2 interacted with GSK-3beta and induced its ubiquitination and subsequent proteasomal degradation, and hence upregulated beta-catenin in Col2a1-Smurf2 transgenic chondrocytes ex vivo. It is therefore likely that Smurf2-mediated upregulation of beta-catenin through induction of proteasomal degradation of GSK-beta in chondrocytes may activate articular chondrocyte maturation and associated alteration of gene expression, the early events of OA.

The contribution of the synovium, synovial derived inflammatory cytokines and neuropeptides to the pathogenesis of osteoarthritis

Osteoarthritis (OA) is one of the most common and disabling chronic joint disorders affecting horses, dogs and humans. Synovial inflammation or synovitis is a frequently observed phenomenon in osteoarthritic joints and contributes to the pathogenesis of OA through formation of various catabolic and pro-inflammatory mediators altering the balance of cartilage matrix degradation and repair. Catabolic mediators produced by the inflamed synovium include pro-inflammatory cytokines, nitric oxide, prostaglandin E(2) and several neuropeptides, which further contribute to the pathogenesis of OA by increasing cartilage degradation. Recent studies suggest that substance P, corticotropin-releasing factor, urocortin and vasoactive intestinal peptide may also be involved in OA development, but the precise role of these neuropeptides in the pathogenesis of OA is not known. Since increased production of matrix metalloproteinases by the synovium is stimulated by pro-inflammatory cytokines, future anti-inflammatory therapies should focus on the synovium as a means of controlling subsequent inflammatory damage.

Platelet derived growth factor-AB enhances knee meniscal cell activity in vitro

Meniscal healing especially in the inner avascular region has always been a major challenge. In this study we investigated the potential for platelet derived growth factor-AB (PDGF-AB) to promote meniscal tissue regeneration in the inner (avascular), middle, and outer (vascular) zones of the meniscus. Various concentrations of PDGF-AB were tested on sheep meniscal cell cultures. We used the radioactive thymidine uptake assay to assess cell proliferation, and the radioactive sulphur and proline uptake assays and Blyscan assay to assess matrix formation. In general, PDGF-AB stimulated both cell proliferation and matrix formation by cells from all meniscal zones. PDGF-AB at a concentration of 100 ng/ml increased cell proliferation and matrix formation by eight and four fold respectively, by fibrochondrocytes cultured from all meniscal zones (p<0.001). These results indicate that fibrochondrocytes present within the avascular region of the meniscus have the ability to proliferate and form new matrix when exposed to anabolic cytokines such as PDGF-AB.

In vivo local administration of osteogenic protein-1 increases structural properties of the overstretched anterior cruciate ligament with partial midsubstance laceration

We report the effects of local administration of osteogenic protein-1 on the biomechanical properties of the overstretched anterior cruciate ligament in an animal model. An injury in the anterior cruciate ligament was created in 45 rabbits. They were divided into three equal groups. In group 1, no treatment was applied, in group II, phosphate-buffered saline was applied around the injured ligament, and in group III, 12.5 μg of osteogenic protein-1 mixed with phosphate-buffered saline was applied around the injured ligament. A control group of 15 rabbits was assembled from randomly-selected injured knees from among the first three groups. Each rabbit was killed at 12 weeks.

The maximum load and stiffness of the anterior cruciate ligament was found to be significantly greater in group III than either group 1 (p = 0.002, p = 0.014) or group II (p = 0.032, p = 0.025). The tensile strength and the tangent modulus of fascicles from the ligament were also significantly greater in group III than either group I (p = 0.002, p = 0.0174) or II (p = 0.005, p = 0.022).

The application of osteogenic protein-1 enhanced the healing in the injured anterior cruciate ligament, but compared with the control group the treated ligament remained lengthened. The administration of osteogenic protein-1 may have a therapeutic role in treating the overstretched anterior cruciate ligament.

Chitosan and its derivatives for tissue engineering applications

Tissue engineering is an important therapeutic strategy for present and future medicine. Recently, functional biomaterial researches have been directed towards the development of improved scaffolds for regenerative medicine. Chitosan is a natural polymer from renewable resources, obtained from shell of shellfish, and the wastes of the seafood industry. It has novel properties such as biocompatibility, biodegradability, antibacterial, and wound-healing activity. Furthermore, recent studies suggested that chitosan and its derivatives are promising candidates as a supporting material for tissue engineering applications owing to their porous structure, gel forming properties, ease of chemical modification, high affinity to in vivo macromolecules, and so on. In this review, we focus on the various types of chitosan derivatives and their use in various tissue engineering applications namely, skin, bone, cartilage, liver, nerve and blood vessel.

Porous gelatin-chondroitin-hyaluronate tri-copolymer scaffold containing microspheres loaded with TGF-beta1 induces differentiation of mesenchymal stem cells in vivo for enhancing cartilage repair

The aim of the study was to produce a novel porous gelatin-chondroitin-hyaluronate scaffold in combination with a controlled release of transforming growth factor beta1 (TGF-beta1), which induced the differentiation of mesenchymal stem cells (MSCs) in vivo for enhancing cartilage repair. Gelatin microspheres loaded with TGF-beta1 (MS-TGFbeta1) showed a fast release at the initial phase (37.4%), and the ultimate accumulated release was 83.1% by day 18. The autologous MSCs seeded on MS-TGFbeta1/scaffold were implanted to repair full-thickness cartilage defects in rabbits as in vivo differentiation repair group, while MSCs differentiated in vitro were seeded on scaffold without MS-TGFbeta1 to repair the contra lateral cartilage defects (n = 30). Fifteen additional rabbits without treatment for defects were used as control. Histology observation showed that the in vivo differentiation repair group had better chondrocyte morphology, integration, continuous subchondral bone, and much thicker newly formed cartilage layer when compared to in vitro differentiation repair group 12 and 24 weeks, postoperatively. There was a significant difference in histological grading score between these two experimental groups, and both showed much better repair than that of the control. The present study implied that the novel scaffold with MS-TGFbeta1 might serve as a new way to induce the differentiation of MSCs in vivo to enhance the cartilage repair.

A review of the effects of insulin-like growth factor and platelet derived growth factor on in vivo cartilage healing and repair

Growth factors may enhance current cartilage repair techniques via multiple mechanisms including recruitment of chondrogenic cells (chemotaxis), stimulation of chondrogenic cell proliferation (mitogenesis) and enhancement of cartilage matrix synthesis. Two growth factors that have been studied in cartilage repair are insulin-like growth factor (IGF) and platelet derived growth factor (PDGF). IGF plays a key role in cartilage homeostasis, balancing proteoglycan synthesis and breakdown. Incorporating IGF into a fibrin clot placed in an equine cartilage defect improved the quality and quantity of repair tissue and reduced synovial inflammation. PDGF is a potent mitogenic and chemotactic factor for all cells of mesenchymal origin, including chondrocytes and mesenchymal stem cells. Resting zone chondrocytes cultured with PDGF demonstrated increased cell proliferation and proteoglycan production, while maturation of these cells along the endochondral pathway was inhibited. Pretreating chondrocytes with PDGF promotes heterotopic cartilage formation in the absence of any mechanical stimulus. PDGF has also been shown to be a potent stimulator of meniscal cell proliferation and migration. These studies and others suggest a potential role for these potent biological regulators of chondrocytes in cartilage repair. More work needs to be performed to define their appropriate dosing and the optimum delivery method. Combining tissue growth factors with a biological matrix can provide a physical scaffold for cell adhesion and growth as well as a means to control the release of these potent molecules. This could result in biological devices that enhance the predictability and quality of current cartilage repair techniques.

Porous chitosan-gelatin scaffold containing plasmid DNA encoding transforming growth factor-β1 for chondrocytes proliferation

Cartilage defects as a result of disease or injury have a very limited ability to heal spontaneously. Recently, tissue engineering and local therapeutic gene delivery systems have been paid much attention in the cartilage natural healing process. Gene-activated matrix (GAM) blends these two strategies, serving as local bioreactor with therapeutic agents expression and also providing a structural template to fill the lesion defects for cell adhesion, proliferation and synthesis of extracellular matrix (ECM). In the current study, we used chitosan-gelatin complex as biomaterials to fabricate three-dimensional scaffolds and plasmid DNA were entrapped in the scaffolds encoding transforming growth factor-beta1 (TGF-beta1), which has been proposed as a promoter of cartilage regeneration for its effect on the synthesis of matrix molecules and cell proliferation. The plasmid DNA incorporated in the scaffolds showed a burst release in the first week and a sustained release for the other 2 weeks. The gene transfectd into chondrocytes expresses TGF-beta1 protein stably in 3 weeks. The histological and immunohistochemical results confirmed that the primary chondrocytes cultured into the chitosan-gelatin scaffold maintained round and owned characters of high secretion of specific ECM. From this study, it can be concluded that this gene-activated chitosan-gelatins matrix has a potential in the application of cartilage defects regeneration.

TAK1 downregulation reduces IL-1β induced expression of MMP13, MMP1 and TNF-alpha

The paper provides evidence that transforming growth factor-beta activated kinase 1 (TAK1, MEKK7), a downstream mediator of IL-1beta signal transduction, plays an important role in the regulation of catabolic events and inflammatory processes in the context of degenerative joint diseases. We investigated the expression of TAK1 in human articular chondrocytes and in the murine growth plate by cDNA array, quantitative RT-PCR and immunohistochemistry, respectively. The human chondrosarcoma cell line SW1353 was stimulated with the proinflammatory cytokine IL-1beta. The subsequent expression of proteolytic enzymes and proinflammatory cytokines was quantified. TAK1 specific siRNA was used to study the influence of TAK1 downregulation on the expression of MMP-13, MMP1 and TNF-alpha. As a result we demonstrated the expression of TAK1 in normal and osteoarthritic human articular cartilage. Expression of TAK1 in the hypertrophic zone of the growth plate gave us a first evidence for a catabolic function of TAK1 concerning cartilage metabolism. By gene suppression with RNAi technology we could show that TAK1 downregulation leads to a 60-70% reduced release of TNF-alpha, a 40-50% reduced release of MMP13, and a 20-30% reduction of MMP1 release. As TNF-alpha is a main player in inflammatory processes, and MMP13 is one of the major proteases involved in cartilage degradation, our results suggests that TAK1 has an important regulatory role in the context of degenerative joint diseases and thus is an attractive drug target in attempts to reduce inflammation and suppress structural changes in OA induced by IL-1beta.

Targeted disruption of Mig-6 in the mouse genome leads to early onset degenerative joint disease

Degenerative joint disease, also known as osteoarthritis, is the most common joint disorder in human beings. The molecular mechanism underlying this disease is not fully understood. Here, we report that disruption of mitogen-inducible gene 6 (Mig-6) in mice by homologous recombination leads to early onset degenerative joint disease, which is revealed by simultaneous enlargement and deformity of multiple joints, degradation of articular cartilage, and the development of bony outgrowths or osteophyte formation within joint space. The osteophyte formation appears to be derived from proliferation of mesenchymal progenitor cells followed by differentiation into chondrocytes. Absence of the Rag2 gene does not rescue the joint phenotype, excluding a role for the acquired immune system in the development of this disease. Our results provide insight into the mechanism of osteoarthritis by showing that loss of Mig-6 leads to early onset of this disease, implying that this gene or its pathway is important in normal joint maintenance. Because of the striking similarity of osteoarthritis in humans and mice, the Mig-6 mutant mouse should provide a useful animal model for studying the mechanism of this disease and for testing drugs or therapies for treating osteoarthritis.

Obesity and the female sex, risk factors for knee osteoarthritis that may be attributable to systemic or local leptin biosynthesis and its cellular effects

Obesity and the female sex represent significant risk factors for osteoarthritis (OA). Few studies have demonstrated a metabolic link between obesity and OA, strengthening the likelihood that biomechanical factors mediate this relationship, possibly via the redistribution of increased body mass to weight-bearing joints. However, it is less plausible that the biomechanical factors that contribute toward the incidence of OA at weight-bearing joints, such as the knee, are similar to those at non-weight bearing joints, such as in the hand. This may suggest that non-examined or unidentified biomechanical and/or systemic factors may be important contributors to the aetiology of OA. Recent developments that have helped to better appreciate the pathophysiology of obesity offer new hope to understanding the link between obesity and OA. The discovery of the obesity gene (ob) and its product leptin may have important implications for the onset and progression of OA. For instance, the greater total body fat of the average adult female may partially account for the gender disparity toward OA, given that females theoretically demonstrate higher levels of adipose derived systemic leptin concentrations than their male counterparts. However, while it was previously thought that adipose cells were only capable of leptin production, osteoblasts and chondrocytes are also capable of leptin synthesis and secretion, inferring that local leptin production may be of great importance. For instance, significant levels of leptin were observed in the cartilage and osteophytes of people with OA, yet few chondrocytes produced leptin in the cartilage of healthy people. Leptin has also been demonstrated to induce anabolic activity in the chondrocytes of rats, which may ultimately confer structural joint changes. This paper hypothesizes that leptin may be an unexamined systemic or local factor that may mediate the metabolic link between obesity and OA and partially account for the gender disparity toward the disease.

The effect of growth factors on biomechanical properties of the bone-patellar tendon-bone graft after anterior cruciate ligament reconstruction: a canine model study

BACKGROUND

No studies have dealt with the effect of growth factors on the free tendon autograft in anterior cruciate ligament reconstruction.

HYPOTHESIS

Application of exogenous transforming growth factor-beta and epidermal growth factor may affect the structural properties and histology of the bone-patellar tendon-bone autograft after anterior cruciate ligament reconstruction.

STUDY DESIGN

Controlled laboratory study.

METHODS

Twenty dogs underwent anterior cruciate ligament reconstruction with the autogenous bone-patellar tendon-bone graft in bilateral knees. In 10 animals, 12 ng transforming growth factor-beta and 300 ng epidermal growth factor mixed with fibrin sealant of 0.6 mL were applied to the left knee. In the remaining 10 dogs, fibrin sealant alone was applied to the left knee. No additional treatments were applied to the right knee.

RESULTS

The growth factor application increased the stiffness and maximum failure load of the femur-graft-tibia complex at 12 weeks (P =.016 and P =.012, respectively); the sham treatment did not significantly affect them. Histologically, most of the cells in the grafts treated with growth factors had spindle-shaped nuclei; cells in the other grafts had round-shaped nuclei.

CONCLUSIONS

Application of transforming growth factor-beta and epidermal growth factor improves the structural properties of the autograft after anterior cruciate ligament reconstruction in the canine model.

CLINICAL RELEVANCE

Application of growth factors is a possible strategy to prevent graft deterioration in anterior cruciate ligament reconstruction.

Promoting the proliferative and synthetic activity of knee meniscal fibrochondrocytes using basic fibroblast growth factor in vitro

BACKGROUND

Meniscal tears situated within the inner avascular region do not heal despite suturing. New approaches need to be developed to augment surgical repair.

HYPOTHESIS

To demonstrate that basic fibroblast growth factor, used as a single agent or in combination with serum, stimulates the activity of fibrochondrocytes by enhancing proliferation and extracellular matrix synthesis in all meniscal zones, including the inner (avascular) zone of the meniscus.

STUDY DESIGN

Controlled laboratory study.

METHODS

Monolayer cell cultures were prepared from the inner, middle, and outer zones of the lateral meniscus. Various concentrations of basic fibroblast growth factor were used in the presence or absence of 10% fetal calf serum. The authors measured the uptake of radiolabeled thymidine to assess cell proliferation and radioactive sulfur and proline to assess extracellular matrix formation.

RESULTS

Overall, basic fibroblast growth factor-stimulated cells from all meniscal zones to proliferate and to form new extra-cellular matrix (P <.05). The basic fibroblast growth factor (in the absence of serum) increased DNA formation and protein synthesis by cells from the inner meniscal zone by 7- and 15-fold, respectively (P <.001).

CONCLUSIONS

These results indicate that meniscal cells and, more important, cells from the avascular zone are capable of responding favorably to the addition of basic fibroblast growth factor by expressing their intrinsic potential to proliferate and generate new extracellular matrix.

CLINICAL RELEVANCE

The results suggest that it may be possible to augment surgical repair of the meniscus in the future.

Reduction of osteophyte formation and synovial thickening by adenoviral overexpression of transforming growth factor ?/bone morphogenetic protein inhibitors during experimental osteoarthritis

OBJECTIVE

Osteoarthritis (OA) is a joint disease characterized by osteophyte development, fibrosis, and articular cartilage damage. Effects of exogenous transforming growth factor beta (TGFbeta) isoforms and bone morphogenetic proteins (BMPs) suggest a role for these growth factors in the pathogenesis of OA. The aim of this study was to elucidate the role of endogenous TGFbeta and BMP during papain-induced OA-like changes in mice.

METHODS

We used adenoviral overexpression of TGFbeta and BMP antagonists to block growth factor signaling. An adenovirus expressing a secreted, pan-specific TGFbeta antagonist called murine latency-associated peptide 1 (mLAP-1) was used. In addition, we used intracellular inhibitory Smad6 as a BMP antagonist and Smad7 as a TGFbeta/BMP inhibitor. Papain was injected into the knee joints of C57BL/6 mice to induce osteophyte development, synovial thickening, and articular cartilage proteoglycan (PG) loss.

RESULTS

Intraarticular injection of papain caused increased protein expression of several TGFbeta and BMP isoforms in synovium and cartilage. Adenovirus transfection into the joint resulted in a strong expression of the transgenes in the synovial lining. Overexpression of mLAP-1, Smad6, and Smad7 led to a significant reduction in osteophyte formation compared with that in controls. Smad6 and Smad7 overexpression also significantly decreased synovial thickening. Furthermore, the secreted TGFbeta inhibitor mLAP-1 increased articular cartilage PG loss.

CONCLUSION

Our results indicate a pivotal role of endogenous TGFbeta in the development of osteophytes and synovial thickening, implicating endogenous TGFbeta in the pathogenesis of OA. In contrast, the prevention of cartilage damage by endogenous TGFbeta signifies the protective role of TGFbeta in articular cartilage. This is the first study to demonstrate that endogenous BMPs are involved in osteophyte formation and synovial thickening in experimental OA.

Evidence for a key role of leptin in osteoarthritis

OBJECTIVE

To evaluate the contribution of leptin (an adipose tissue-derived hormone) to the pathophysiology of osteoarthritis (OA), by determining the level of leptin in both synovial fluid (SF) and cartilage specimens obtained from human joints. We also investigated the effect of leptin on cartilage, using intraarticular injections of leptin in rats.

METHODS

Leptin levels in SF samples obtained from OA patients undergoing either knee replacement surgery or knee arthroscopy were measured by enzyme-linked immunosorbent assay. In addition, histologic sections of articular cartilage and osteophytes obtained during surgery for total knee replacement were graded using the Mankin score, and were immunostained using antibodies to leptin, transforming growth factor beta (TGFbeta), and insulin-like growth factor 1 (IGF-1). For experimental studies, various doses of leptin (10, 30, 100, and 300 microg) were injected into the knee joints of rats. Tibial plateaus were collected and processed for proteoglycan synthesis by radiolabeled sulfate incorporation, and for expression of leptin, its receptor (Ob-Rb), and growth factors by reverse transcriptase-polymerase chain reaction and immunohistochemical analysis.

RESULTS

Leptin was observed in SF obtained from human OA-affected joints, and leptin concentrations correlated with the body mass index. Marked expression of the protein was observed in OA cartilage and in osteophytes, while in normal cartilage, few chondrocytes produced leptin. Furthermore, the pattern and level of leptin expression were related to the grade of cartilage destruction and paralleled those of growth factors (IGF-1 and TGFbeta1). Animal studies showed that leptin strongly stimulated anabolic functions of chondrocytes and induced the synthesis of IGF-1 and TGFbeta1 in cartilage at both the messenger RNA and the protein levels.

CONCLUSION

These findings suggest a new peripheral function of leptin as a key regulator of chondrocyte metabolism, and indicate that leptin may play an important role in the pathophysiology of OA.

Porous chitosan scaffold containing microspheres loaded with transforming growth factor-beta1: implications for cartilage tissue engineering

Damaged articular cartilage, caused by traumatic injury or degenerative diseases, has a limited regenerative capacity and frequently leads to the onset of osteoarthritis. As a promising strategy for the successful regeneration of long-lasting hyaline cartilage, tissue engineering has received increasing recognition. In this study, we attempted to design a novel type of porous chitosan scaffold, containing transforming growth factor-beta1 (TGF-beta1), to enhance chondrogenesis. First, to achieve a sustained release of TGF-beta1, chitosan microspheres loaded with TGF-beta1 (MS-TGFs) were prepared by the emulsion method, in the presence of tripolyphosphate; with an identical manner, microspheres loaded with BSA, a model protein, were also prepared. Both microspheres containing TGF-beta1 and BSA had spherical shapes with a size ranging from 0.2 to 1.5 microm. From the release experiments, it was found that both proteins were slowly released from the microspheres over 5 days in a PBS solution (pH 7.4), in which the release rate of TGF-beta1 was much lower than that of BSA. Second, MS-TGFs were seeded onto the porous chitosan scaffold, prepared by the freeze-drying method, to observe the effect on the proliferation and differentiation of chondrocytes. It was obviously demonstrated from in vitro tests that, compared to the scaffold without MS-TGF, the scaffold containing MS-TGF significantly augments the cell proliferation and production of extracellular matrix, indicating the role of TGF-beta1 released from the microspheres. These results suggest that the chitosan scaffold containing MS-TGF possesses a promising potential as an implant to treat cartilage defects.

Large scale protein production of the extracellular domain of the transforming growth factor-beta type II receptor using the Pichia pastoris expression system

To study the (patho)physiological role of transforming growth factor-beta (TGF-beta), potent and selective inhibitors are necessary. Since TGF-beta signaling is initiated by the high affinity binding to the type II receptor (RII), the extracellular part of RII (solRII) can function as a TGF-beta antagonist. SolRII was cloned and large-scale protein synthesis was performed in the yeast Pichia pastoris expression system. Our results indicate that via this system, high levels of pure concentrated solRII can be obtained. Moreover, purified solRII is an active protein as shown by ELISA and bioassay. In conclusion, our large-scale protein expression procedure results in high quantities of purified solRII, which is a powerful tool to study the natural role of TGF-beta.

Advances in drug delivery for articular cartilage

The complex structure of articular cartilage, the connective tissue lining diarthrodial joints, enables this tissue to dissipate compressive loads but also appears to hinder its repair ability. At best, both natural and surgical repair attempts replace the highly ordered extracellular matrix of native articular cartilage with fibrous repair tissue of inferior mechanical properties. Numerous bioactive molecules closely regulate the cellular processes in healthy and degenerative articular cartilage. Accordingly, this review outlines the roles of important signaling molecules in cartilage tissue. In addition, drug delivery strategies, aimed at utilizing these bioactive agents to prevent inflammation, to regulate extracellular matrix metabolism, and to control cellular activities, are discussed. As scientists gain further insight into the complex signaling cascades of articular cartilage, continued refinement of drug delivery systems is necessary to develop effective clinical therapies for articular cartilage repair.

Inhibition of endogenous TGF-beta during experimental osteoarthritis prevents osteophyte formation and impairs cartilage repair

Osteoarthritis has as main characteristics the degradation of articular cartilage and the formation of new bone at the joint edges, so-called osteophytes. In this study enhanced expression of TGF-beta1 and -beta3 was detected in developing osteophytes and articular cartilage during murine experimental osteoarthritis. To determine the role of endogenous TGF-beta on osteophyte formation and articular cartilage, TGF-beta activity was blocked via a scavenging soluble TGF-beta-RII. Our results clearly show that inhibition of endogenous TGF-beta nearly completely prevented osteophyte formation. In contrast, treatment with recombinant soluble TGF-beta-RII markedly enhanced articular cartilage proteoglycan loss and reduced the thickness of articular cartilage. In conclusion, we show for the first time that endogenous TGF-beta is a crucial factor in the process of osteophyte formation and has an important function in protection against cartilage loss.

Recent advances in TGF-beta effects on chondrocyte metabolism. Potential therapeutic roles of TGF-beta in cartilage disorders

Novel approaches to treat osteoarthritis are required and progress in understanding the biology of cartilage disorders has led to the use of genes whose products stimulate cartilage repair or inhibit breakdown of the cartilaginous matrix. Among them, transforming growth factor-beta (TGF-beta) plays a significant role in promoting chondrocyte anabolism in vitro (enhancing matrix production, cell proliferation, osteochondrogenic differentiation) and in vivo (short-term intra-articular injections lead to increased bone formation and subsequent cartilage formation, beneficial effects on osteochondrogenesis). In vivo induction of the expression of TGF-beta and the use of gene transfer may provide a new approach for treatment of osteoarthritic lesions.

Growth-factor-induced healing of partial-thickness defects in adult articular cartilage

OBJECTIVE

We have previously shown (Hunziker and Rosenberg, J Bone Joint Surg 1996;78A:721-33) that synovial cells can be induced to migrate into partial-thickness articular cartilage defects, therein to proliferate and subsequently to deposit a scar-like tissue. We now wished to ascertain whether these synovial cells could be stimulated to transform into chondrocytes, and thus to lay down cartilage tissue, by the timely introduction of a differentiation factor.

DESIGN

Partial-thickness defects were created in the knee-joint cartilage of adult miniature pigs. These were then filled with a fibrin matrix containing a free chemotactic/mitogenic factor and a liposome-encapsulated chondrogenic differentiation one. Tissue was analyzed (immuno)histochemically at 2, 6 and 12 months.

RESULTS

Defects became filled with cartilage-like tissue which registered positive for all major cartilage-matrix components; it remained compositionally stable throughout the entire follow-up period.

CONCLUSION

Although still requiring considerable refinement, our one-step, growth-factor-based treatment strategy has the basic potential to promote intrinsic healing of partial-thickness articular cartilage defects, thus obviating the need for transplanting cells or tissue.

Pretreatment with platelet derived growth factor-BB modulates the ability of costochondral resting zone chondrocytes incorporated into PLA/PGA scaffolds to form new cartilage in vivo

Optimal repair of chondral defects is likely to require both a suitable population of chondrogenic cells and a biodegradable matrix to provide a space-filling structural support during the early stages of cartilage formation. This study examined the ability of chondrocytes to support cartilage formation when incorporated into biodegradable scaffolds constructed from copolymers (PLG) of polylactic acid (PLA) and polyglycolic acid (PGA) and implanted in the calf muscle of nude mice. Scaffolds were fabricated to be more hydrophilic (PLG-H) or were reinforced with 10% PGA fibers (PLG-FR), increasing the stiffness of the implant by 20-fold. Confluent primary cultures of rat costochondral resting zone chondrocytes (RC) were loaded into PLG-H foams and implanted intramuscularly. To determine if growth factor pretreatment could modulate the ability of the cells to form new cartilage, RC cells were pretreated with recombinant human platelet derived growth factor-BB IPDGF-BB) for 4 or 24 h prior to implantation. To assess whether scaffold material properties could affect the ability of chondrogenic cells to form cartilage, RC cells were also loaded into PLG-FR scaffolds. To determine if the scaffolds or treatment with PDGF-BB affected the rate of chondrogenesis, tissue at the implant site was harvested at four and eight weeks post-operatively, fixed, decalcified and embedded in paraffin. Sections were obtained along the transverse plane of the lower leg, stained with haematoxylin and eosin, and then assessed by morphometric analysis for area of cartilage, area of residual implant, and area of fibrous connective tissue formation (fibrosis). Whether or not the cartilage contained hypertrophic cells was also assessed. The amount of residual implant did not change with time in any of the implanted tissues. The area occupied by PLG-FR implants was greater than that occupied by PLG-H implants at both time points. All implants were surrounded by fibrous connective tissue, whether they were seeded with RC cells or not. The amount of fibrosis was reduced at eight weeks for both implant types. When RC cells were present, the amount of fibrosis was less than seen in cell-free scaffolds. Pretreatment with PDGF-BB caused a slightly greater degree of fibrosis at four weeks than was seen if untreated cells were used in the implants. However, at eight weeks, if the cells had been exposed to PDGF-BB for 24 h, fibrosis was comparable to that seen associated with cell-free scaffolds. The cells supported an equivalent area of cartilage formation in both scaffolds. PDGF-BB caused a time-dependent decrease in cartilage formation at four weeks, but at eight weeks, there was a marked increase in cartilage formation in PDGF-BB-treated cells that was greatest in cells exposed for 4 h compared to those exposed for 24 h. Moreover, PDGF-BB decreased the formation of hypertrophic cells. The results indicate that in this model, RC cells produce cartilage; pretreatment of the RC cells with PDGF-BB promotes retention of a hyaline-like chondrogenic phenotype; and the material properties of the implant do not negatively impact on the ability of the cells to support chondrogenesis.

Osteoarthritis-like changes in the murine knee joint resulting from intra-articular transforming growth factor-beta injections

OBJECTIVE

To examine the impact of prolonged TGF-beta exposure on cartilage and ligamentous joint structures in vivo, to investigate involvement of TGF-beta in osteoarthritis pathology.

METHODS

TGF-beta was injected into murine knee joints once or repeatedly, whereafter articular cartilage proteoglycan (PG) synthesis and content, and histological changes in knee joints were studied over a 2-month period.

RESULTS

A single injection of TGF-beta stimulated patellar cartilage PG synthesis for 3 weeks and PG content for 2 weeks. Triple TGF-beta injections prolonged the increase in PG content to 3 weeks. Patellar cartilage showed no histological abnormalities at 1 and 2 months after the last injection. In contrast, 2 months after triple TGF-beta injections the superficial layer of tibial cartilage still had an increased proteoglycan content, while severe PG depletion was found in deeper layers of the posterior part of the lateral tibia in particular. Eventually, lesions occurred at the level of the tide-mark, exactly the site where cartilage is torn off in experimental and spontaneous osteoarthritis in mice. Additionally, multiple TGF-beta injections induced formation of chondroid structures along the margins of articular cartilage. These chondroid structures were transformed into osteophytes via endochondral ossification. Formation of chondroid tissue was also observed in collateral ligaments.

CONCLUSION

Multiple intra-articular injections of TGF-beta induce changes in articular cartilage and surrounding tissues that have strong resemblance to features of experimental and spontaneous osteoarthritis in mice, suggesting a role for TGF-beta in the OA process.

The long-term effect of a short course of transforming growth factor-beta1 on rat articular cartilage

The long-term effect of 3 days' topical administration of TGF-beta1 on unloaded articular cartilage in growing rats was investigated. Three to five rats were sacrificed on days 15, 30, 45, 60 and 90 after the last injection and the patellas were subjected to light and electron microscopic evaluation. The patellas showed age-related changes when entering the maturation phase. Absence of a hypertrophic zone and formation of a subchondral bone plate were observed in both treated rats and controls from that time point. Reduction of total cell amount was observed between older and younger patellas in both treated rats and controls. TGF-beta1 treatment resulted in accelerated maturation and ageing. Furthermore, the administration of TGF-beta1 resulted in a higher unmineralized cartilage with an increased total amount of cells in the intermediate zone. Matrix areas showing ultrastructural features of disturbed matrix composition were seen in the deeper part of this zone at all time points, but in the treated patellas only. The present results indicate that TGF-beta1 treatment may induce changes in articular cartilage in some respects similar to those seen in the early stages of degenerative and inflammatory joint diseases.

Differentiated cellular function in fetal chondrocytes cultured with insulin-like growth factor-I and transforming growth factor-beta

This study examined fetal chondrocyte proliferation and function following exposure to transforming growth factor-beta and insulin-like growth factor-I. Fetal equine articular chondrocytes of the early third-trimester were isolated and cultured in monolayer conditions, then exposed to 0, 1, 5, or 10 ng/ml transforming growth factor-beta or 0, 10, 50, or 100 ng/ml insulin-like growth factor-I for 48 hours. Proliferative responses were assessed by cell counts and [3H]thymidine uptake into precipitable DNA. Differentiated chondrocyte metabolic activity was determined by sulfated glycosaminoglycan quantitation, 35[SO4] incorporation into precipitable glycosaminoglycan, and proteoglycan molecular sizing by CL-2B column chromatography. Morphological changes seen on phase-contrast microscopy included a larger proportion of rounded cells in monolayer cultures supplemented with insulin-like growth factor-I and cytotoxic changes in cells treated with transforming growth factor-beta. Both insulin-like growth factor-I and transforming growth factor-beta resulted in significant elevations of [3H]thymidine uptake; however, cell numbers did not rise sufficiently over the 48-hour culture period to reach significant levels. Maximum mitogenic responses were evident at 50 and 100 ng/ml insulin-like growth factor-I and 5 ng/ml transforming growth factor-beta. The production of proteoglycan was also enhanced (435%) by exposure to 50 ng/ml insulin-like growth factor-I, and an increased proportion of larger proteoglycan monomer species was evident in cultures treated with 50 and 100 ng/ml insulin-like growth factor-I. A similar dose-response was also evident in cultures treated with transforming growth factor-beta (maximal 164% increase with 5 ng/ml), although the presence of serum in the culture medium altered the pattern of enhanced proteoglycan synthesis to favor the lower concentration of 1 ng/ml (191%). Additionally, larger proteoglycan molecules were synthesized in response to high concentrations of transforming growth factor-beta in serum-free cultures. Significant biochemical changes resulted from the addition of transforming growth factor-beta to fetal chondrocyte cultures; however, monolayer cultures that were treated with transforming growth factor-beta and supplemented with serum began to develop cellular toxicity, including nuclear pyknosis and cytoplasmic fragmentation. Degenerative cellular changes were not evident in cultures treated with insulin-like growth factor-I, and significant differentiated metabolic activity resulted from the presence of insulin-like growth factor-I in the culture medium. These data suggest that the responses of fetal chondrocytes to insulin-like growth factor-I and transforming growth factor-beta were enhanced compared with the responses of chondrocytes derived from postnatal animals and that these metabolically active cells can be primed by endogenous or exogenous growth factors to provide enhanced articular function and repair.

Ultrastructural studies on the effect of transforming growth factor-beta 1 on rat articular cartilage

The destruction of articular cartilage in degenerative and inflammatory joint disease reflects an imbalance between synthesis and degradation of the structural components of the tissue. In previous, mainly in vitro studies, TGF-beta has been shown not only to play a role in controlling the synthesis of matrix components such as collagen and proteoglycans but also to influence their degradation. To elucidate the effect of local administration of TGF-beta on unloaded articular cartilage in growing rats, three animals were given intraarticular injections of TGF-beta for three consecutive days and sacrificed on the fourth. Perfusion fixation was combined with qualitative and quantitative evaluation (stereology) both at the light and electron microscopic level. Local administration of TGF-beta resulted in a decrease in height of the hypertrophic zone. Furthermore, the volume density of cells decreased and cells with a distinct morphology designated stellate cells appeared in this zone. In the same compartment, TGF-beta administration resulted in decreased pericellular collagen volume density while the volume density increased in the intermediate zone. The results of our investigation support and extend previous observations: TGF-beta does not only modulate the metabolism of articular cartilage in general, but the effect is targeted to specific subcompartments of the matrix. However, the result of this acute effect on the long-term function of the tissue remains to be elucidated.